I'm a husband, father, author, cyclist, sailor, travel addict, and former Silicon Valley software engineer. I've written 3 books and actively review books on this blog.
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The book's written in a strange, twisted fashion. In summary, the KonMari method of tidying up is fairly straightforward:

Do your tidying up project all in one go. Don't try to do it incrementally.

Get rid of stuff that doesn't bring you joy. (This one is bizarre, since toilet paper doesn't bring me joy but I'm not getting rid of it from my house, but I get her point --- tidying up must start with getting rid of stuff)

Get rid of stuff in inverse order of difficulty (i.e., easiest stuff first). That means clothes, books/CDs first, then personal effects and momentos last. That's so you don't get distracted, and also because you'll be practiced at throwing out stuff by the time you get to the hard part.

Each person in the family should have their own storage, and all their own storage should be in one place, rather than being scattered in multiple places. This ensures when you're searching for something your'e only searching for it where you are.

Don't tidy for other people. If you want other people in your family to be more tidy, start by being tidy yourself.

Store clothing folded, don't use hangers except for stuff that needs it. Don't rotate clothing in and out of season. Just keep it organized by weather and use case.

In shelves, store things in order of height, with increasing height to the right. ("Up and to the right.")

Throw out documents as soon as you're done with them. For warranties, store everything in one folder and throw out stuff that's out of date. Throw out manuals, boxes, etc. Forget about resale value and reboxing when selling.

Don't worry about throwing out stuff you actually need. You can usually buy it again later if you really need it.

Yup, I just summarized everything in one check list. The rest of the book is bizarre nonsense like her strange statement that if you roll up socks, they won't be properly rested when you next put them on. (WTF!) Then she makes a big deal out of thanking your stuff. Sorry, things are things. I like my bicycles, but I didn't make a big deal out of the frame when it failed. I stripped it, sent it back to the manufacturer, and got a new one.

The book has some nice ideas, but she could have made it much shorter and easier to read and put into practice. In the last chapter she finally admits that despite her prior hyperbole about how tidying will make a massive change in your life, her experience is twisted by selection bias: the kind of people who pay her fees for her assistance in tidying up their house are the kind of people who would be predisposed to attributing all sorts of magic career changes and better health to the KonMari method.

All in all, the book has interesting ideas, but if you'd read this blog post you probably got them all! I just saved you 4 hours of reading/listening.